1. Field of the Invention
The present invention relates to a communication apparatus, a method of controlling the same, and a storage medium.
2. Description of the Related Art
In addition to facsimile (to be referred to as FAX hereinafter) communication using a conventional public switched telephone network (PSTN), there is provided FAX communication using a high-speed network such as an IP network. There are two methods for FAX communication using the IP network. One of the methods is to implement, by using a deemed voice, T.30 FAX using the T.30 protocol of ITU-T recommendation. This method is a method of performing communication by converting a T.30 analog signal into a digital signal, and is called T.30 FAX deemed voice communication since communication is performed by deeming a T.30 analog signal a voice signal.
The other method is a communication method called T.38 of ITU-T recommendation, which performs communication without converting a digital signal communicated according to the T.30 protocol. This method can implement higher-speed communication, as compared with T.30. The above-described two methods implement Point-to-Point communication on the IP network using SIP (Session Initiation Protocol) as a call control unit.
Examples of the IP network are a digital public network called an NGN (Next Generation Network) provided by NTT Group in Japan, and a private IP line using an IP private branch exchange (IP-PBX) or the like. In the case of the NGN network, for example, the bandwidth is guaranteed and the security is managed, thereby allowing high-speed secure image communication. Although the communication speed of the conventional PSTN is at most 33.6 Kbps, the NGN guarantees a communication speed of at most 1 Mbps, thereby allowing communication at a speed about 30 times higher than that of the PSTN.
There is provided a method in which an image communication apparatus capable of performing T.38 FAX communication and T.30 FAX deemed voice communication implements an operation of a telephone system on the IP network. In this case, it is possible to perform voice communication and FAX communication by only connecting to the network without connecting to the public switched telephone network (PSTN). To do this, similarly to FAX communication, a handset and a slave are connected to the IP network, and exchanges voice data by transmitting voice packets via the IP network. This is a so-called IP phone, for which ITU-T recommendation G.711 is used as a voice packet encoding method and RTP (Real Time Protocol) is used as a transmission protocol.
To implement a telephone by connecting to the IP network, an SLIC (Subscriber Line Interface Circuit) for connecting the telephone to the IP network is used. The main application purpose of this SLIC is identification of a dial signal from the telephone and the like, ringing control of the telephone, detection of a hooking operation of the telephone, and the like.
To simultaneously connect to a plurality of connection destinations by the PSTN, it is necessary to connect modular cables, the number of which is equal to that of connection destinations. In T.30 FAX deemed voice communication using an IP line, however, it is possible to simultaneously connect to a plurality of connection destinations to perform communications and voice communications by only connecting one network cable. This is called a multi-session connection. In the multi-session environment, with respect to SIP, a connection session starts with an SIP session connection request signal INVITE, and ends with an SIP session disconnection signal BYE. The first connection is the first session, and the next connection is the second session. These connections are not linked with physical lines. By complying with this kind of multi-session connection, it is possible to simultaneously perform a plurality of communications and a plurality of voice communications.
The above-described NGN provides a “multi-channel (the service name in the NGN)” service as a multi-session service. By subscribing to this service, it becomes possible to perform simultaneous communication or voice communication of at most two sessions with one telephone number. The above-described image communication apparatus can be compatible with the multi-session connection. For a conventional image communication apparatus which is compatible with multiple public lines, only one specific line is used for voice communication, and other lines are dedicated to FAX communication. That is, only one telephone can be attached to the image communication apparatus. The main purpose of this is to suppress an increase in cost.
For the same reason, even in the multi-session environment of the IP network, only one telephone can be connected to the image communication apparatus, and it is impossible to simultaneously perform voice communications using two sessions. Such an image communication apparatus can perform two types of communications, that is, (FAX communication+voice communication) and (FAX communication+FAX communication) by simultaneously using two channels. However, this restriction is imposed on only the image communication apparatus, and a plurality of incoming audio calls may be received from the IP network. As will be described later, T.30 FAX deemed voice communication is an incoming audio call. Therefore, only after receiving the incoming call, it can be determined whether the incoming call is voice communication or FAX communication. Therefore, the image communication apparatus which supports only one telephone needs to appropriately control an incoming audio call. For example, assume that when an incoming audio call is received during voice communication with a telephone, the apparatus transits to FAX communication since it can perform only FAX communication. In this case, if the purpose of the incoming call is voice communication, the voice communication cannot be performed, and the incoming call is in vain.
There is also provided a “call waiting (the service name in the NGN)” service as a carrier service. The call waiting service is a service of notifying, when another incoming call is received during voice communication, the user of the incoming call, switching to a communication partner who has called later, and returning to the voice communication with the previous caller. The call waiting service is effective even in the multi-session connection. Even while two sessions are simultaneously used, an incoming call notification is sent from the network during voice communication by using the call waiting service, and it is thus necessary to notify the user of the incoming call. As described above, since only one telephone is connected to the image communication apparatus, it is impossible to notify the user of an incoming call by causing the telephone to ring without any change.
Furthermore, an image communication apparatus which supports voice communication has various reception modes such as an automatic reception mode, FAX/TEL switching mode, and manual reception mode. The automatic reception mode is a mode in which, upon reception of an incoming call, the apparatus automatically transits to FAX reception without causing a connected telephone to respond. The FAX/TEL switching mode is a mode in which the apparatus automatically determines whether an incoming voice communication is FAX communication or telephone communication. In this mode, if a FAX initial identification signal (Calling: CNG signal) is detected after the FAX side establishes a call connection, FAX reception automatically starts. Alternatively, if no CNG signal is detected, the telephone is caused to ring so as to call for the user. The manual reception mode is a mode in which only voice communication is supported. In this mode, the apparatus is not automatically switched to FAX reception, unlike the FAX/TEL switching mode. In this case, however, if the user issues a manual incoming call instruction, or the apparatus has a remote reception function, the apparatus is switched to FAX reception according to the instruction. The remote reception function is a function of switching the main body to FAX reception by an operation (a predetermined dial) of the connected telephone.
A case will be described in which an image communication apparatus having a telephone function and a function of performing FAX communication (T.38 FAX communication and T.30 FAX deemed voice communication) via the IP network by connecting to the IP network receives a call in the above-described reception mode. It is possible to discriminate between an incoming T.38 call and an incoming T.30 FAX deemed voice call or incoming voice communication call by a media attribute sent by a partner apparatus used according to an SIP procedure. The user is notified of an incoming call by an INVITE signal according to the SIP procedure. The contents of the notification include a media attribute (m=the following description included in the INVITE signal). If m=audio, it indicates an incoming T.30 FAX deemed voice call or incoming voice communication call. If m=image or m=application, it indicates an incoming call of T.38 FAX communication. Therefore, upon receiving an incoming T.38 call, the apparatus can automatically transit to T.38 FAX reception from any reception mode. However, the media attribute of an incoming T.30 FAX deemed voice call is the same as that of voice communication, and thus these calls cannot be discriminated. To switch the apparatus to FAX reception in the FAX/TEL switching mode, therefore, it is necessary to determine whether the call is FAX communication after it is connected.
Furthermore, when multi-session connection is supported, two sessions may be used for voice communications instead of FAX communications. In this case, the “call waiting” service provided by the carrier is effective. Since, however, only one telephone is attached to the image communication apparatus, it is necessary to appropriately distribute the voice communications. This distribution technique is described in Japanese Patent Laid-Open No. 2006-295559. The patent literature describes a technique in which if a call in progress is FAX communication, a new incoming call is rejected, and if a call in progress is voice communication, a new incoming call is received. However, the patent literature does not describe multi-session support or an audio session operation in each reception mode.
As described above, even in the case of an image communication apparatus compatible with the multi-session connection, only one telephone is connected at all time and an SLIC for telephone control is provided for only one session. Therefore, in this arrangement, the telephone cannot receive an incoming audio voice communication of the second session while the first session uses the SLIC (telephone function) or an incoming audio call (an incoming call with call waiting) using the call waiting service while the two sessions are fully used. Also, it is impossible to notify the caller of an incoming interrupt call upon receiving an incoming audio call. Furthermore, assume that when an incoming call with call waiting is received while the two sessions are fully used, the partner apparatus is an FAX. In this case, if the image communication apparatus transits to FAX reception, the previous voice communication partner enters a holding state to wait a long time during FAX reception. In addition, the voice communication partner needs to bear an unnecessary communication cost while the voice communication is on hold.